Computers and computer networks are widely used by most all businesses and many individuals to keep records, communicate, produce documents and otherwise manage information. Frequently, the work prepared on a computer is preferably rendered into hard copy form so that it can be stored or sent to another party. For this reason, printers and other printing devices that can render hard copy documents from computer data are critically important.
Inkjet printers are a particularly popular type of printer. In addition to providing a readily affordable printing solution for home or office, inkjet printers have the advantage, among others, of being particularly well suited for color printing.
In an inkjet printer, the image is developed by ejecting ink droplets from the inkjet print head, also called a “pen,” onto a sheet of print medium. Paper is the most common form of print medium, but inkjet printers can print on other media such as cardstock, construction paper, vinyl, transparencies, etc. The ink droplets are ejected from the inkjet print head by, for example, a piezoelectric device that squeezes the ink droplet from the print head, or a thermal member that heats the ink until it is forced out of the print head.
Regardless of the precise method used to expel the ink from the inkjet print head, the ink or toner is dissolved in a volatile, liquid carrier. The carrier facilitates the transfer of the ink from the print head to the print medium. However, the carrier must be evaporated or absorbed by the print medium in order to fix the printed image to the print medium.
Unfortunately, the carrier fluid, when it contacts the print medium, causes the print medium to swell or deform. This is particularly true if the carrier fluid is absorbed by the print medium, but also occurs if the carrier fluid is evaporated from the print medium. This localized swelling of the print medium fibers is a phenomenon known as “cockle.”
Due to cockle formation, the volume of ink and of carrier fluid deposited on the print medium must be carefully controlled so that the cockle does not render the resulting hard copy document unacceptable. If too much ink is deposited on the print medium, or the ink is deposited too quickly, the resulting cockle will likely render the appearance of the printed document unacceptable to the printer user.
Prior art solutions to the cockle problem have involved heating the print medium or print zone before, during and/or after the printing in an attempt to dry the ink and evaporate the carrier fluid before cockle formation. However, it is difficult to supply enough heat to dry the ink quickly enough to prevent cockle formation without causing thermal damage to the print medium. This approach becomes even more difficult as the demand occurs for faster printer and higher output rates. With the print medium moving more quickly to increase output, it becomes that much more difficult to adequately dry a printed sheet to prevent cockle formation. The length of the heating zone can be increased to compensate for the faster print speed, but this causes additional expense and difficulty in manufacturing the printer. Moreover, the amount of heat that can be applied is ultimately limited to a temperature that will not damage the print medium.
Consequently, there is a need in the art for a method and system of preventing cockle formation in an inkjet printer.